Hey Francois,
I’m not sure what the answer to this will be. I’m guessing you’ll have to use a Bitcoin mining calculator and take into account the electricity usage of all miners and Rasberry Pi. Even with 2.7 Th/s it’s still really hard to be profitable with Bitcoin mining. You will probably make somewhere between $30-$50 a month, and that hardly covers the cost of equipment and electricity.
I would also suggest asking this in BitcoinTalk’s mining forum.